1. Field of the Invention
The present invention relates to an image reading apparatus including a document (original) feeder for conveying an original (document) automatically and, more particularly, to an improvement in an original guide at a reading position.
2. Description of Related Art
Conventionally, an image reading apparatus such as a digital copying machine, facsimile machine, or image scanner includes a document feeder which sends out a plurality of stacked originals one by one and conveys each original to a reading position automatically. The image reading apparatus directly reads the original fed to the reading position, i.e., by the so-called flow scanning scheme.
An image reading apparatus which employs this flow scanning scheme includes the first glass platen to read each of the originals which are sequentially supplied by the document feeder, and the second glass platen to place a thick original such as a book on it and read the thick original. When the original moves on the first glass platen, it is read by an image reading unit in a still state which uses a photoelectric converting element, e.g., a CCD. When the original is placed on the second glass plate, it is read by moving the image reading unit.
The document feeder is attached to be able to open/close the upper surface of the image reading apparatus. The original placed on a paper feed tray is conveyed onto the first glass platen along a convey path. The original is scooped up by a scoop-up member which is arranged downstream of the first glass platen to be adjacent to it, and delivered onto a delivery tray along a delivery path. In the document feeder, a convey guide which forms a curved convey path between the first glass platen and the scoop-up member is arranged at a position to oppose the upper surface of the first glass platen. This convey guide can move vertically. A projection formed outside the original convey area of the convey guide abuts against the upper surface of the first glass platen to form a convey path having a predetermined gap between the upper surface of the first glass platen and the convey guide (see Japanese Unexamined Patent Publication No. 2002-14495: patent reference 1). Thus, the original is conveyed within the depth of focus of the image reading unit, and stable conveyance of the original at the reading position is ensured.
In the document feeder, even when the gap between the first glass platen and convey guide is regulated to be small, an impact which occurs when the scoop-up member scoops up the original from the first glass platen, the impact which occurs when the original enters delivery rollers, and the impact which occurs when the trailing edge of the original leaves convey rollers may adversely affect the read image to cause problems such as image blur. In particular, when the leading edge of the original abuts against the scoop-up member or delivery rollers, a reaction force in a direction opposite to a convey direction of the original is applied to the original to hold the original momentarily at the reading position. Then, distortion occurs in the read image.
According to a countermeasure proposed to solve these problems, the gap of that portion of the convey path which is downstream of the first glass platen is made as narrow as possible to moderate the impact during original conveyance, thus suppressing image blur or the like (see Japanese Unexamined Patent Publication No. 2002-171385: patent reference 2, and Japanese Unexamined Patent Publication No. 2002-172618: patent reference 3). In particular, in patent reference 2, the scoop-up member arranged on the upper surface of the image reading apparatus at a position adjacent to the first glass platen is supported swingably. A projection formed on the swingable convey guide is made to abut against the scoop-up member.
In the above arrangement of swinging the scoop-up member, if the biasing force of the convey guide toward the scoop-up member is set larger than the biasing force of the scoop-up member toward the convey guide, the convey guide floats from the first glass platen, and a predetermined gap cannot be ensured between the first glass platen and convey guide. If the biasing force of the scoop-up member toward the convey guide is set smaller than the biasing force of the scoop-up member toward the convey guide, when a firm original such as thick paper is conveyed, the scoop-up member swings to hinder the conveyance. In order to prevent this, each time an original is to be conveyed, the biasing forces of the scoop-up member and convey guide must be adjusted, which is cumbersome. When the convey path is curved, the original is conveyed along the outer guide. To swing the scoop-up member which forms part of the outer guide is not preferable when considering the conveyance stability.